One Rep Max Calculator
Estimate your one-rep max (1RM) from a weight lifted for a number of reps, averaged across seven proven formulas, with a training-load table by rep count.
Your one-rep max (1RM) is the most weight you can lift for a single clean repetition — the benchmark for maximal strength. Rather than attempting a risky true max, this calculator estimates it from a set you can already do for several reps, using seven established prediction formulas.
How it works
Enter the weight you lifted and how many reps you completed. Each formula models the relationship between reps and load differently, so we compute all seven and average them, and show the range so you can see how much they agree:
| Formula | Equation (w = weight, r = reps) |
|---|---|
| Epley | w × (1 + r/30) |
| Brzycki | w × 36 / (37 − r) |
| Lander | 100w / (101.3 − 2.67123r) |
| Lombardi | w × r^0.10 |
| Mayhew et al. | 100w / (52.2 + 41.9·e^(−0.055r)) |
| O’Conner et al. | w × (1 + r/40) |
| Wathan | 100w / (48.8 + 53.8·e^(−0.075r)) |
If you enter a single rep, that weight is your 1RM, so the estimate returns it directly.
Training-load table
Strength programs prescribe work as a percentage of 1RM. The calculator turns your estimate into concrete weights for common rep targets:
| Reps | % of 1RM |
|---|---|
| 1 | 100% |
| 2 | 97% |
| 3 | 94% |
| 5 | 89% |
| 8 | 81% |
| 10 | 75% |
| 12 | 69% |
Getting an accurate estimate
Use a set taken close to failure in the 2–10 rep range — that’s where the formulas are most accurate. Rest fully beforehand, keep your form strict, and re-test every few weeks as you progress. Treat the number as a well-informed estimate, not a guarantee: always warm up and use a spotter before attempting a real maximal lift.
Frequently asked questions
What is a one-rep max (1RM)?
Your one-rep max is the heaviest weight you can lift for a single repetition of an exercise with good form. It's the standard way to measure maximal strength and to set training loads as a percentage of it.
How accurate are 1RM estimates?
For sets in the 2–10 rep range they're quite accurate — usually within a few percent of a true max. Accuracy drops as reps climb above about 10, because the relationship between reps and load becomes less linear. This calculator averages seven formulas to smooth out the differences.
Which formula should I trust?
No single formula is best for everyone, so we show the average of seven (Epley, Brzycki, Lander, Lombardi, Mayhew, O'Conner, and Wathan) plus the range between them. The average is a reliable working estimate; the range tells you how much the formulas disagree.
How do I use the percentages?
Once you know your estimated 1RM, the table shows the weight for common rep targets — e.g. about 89% for 5 reps or 75% for 10. Program your working sets from those loads, and re-test as you get stronger.